Conventionally, particulate matter (hereinafter called PM) and nitrogen oxides (hereinafter called NOx) that promote environmental pollution are included in exhaust gas exhausted from internal combustion engines such as diesel engines, and technologies for removing these substances are known.
Of these, as a technology for removing NOx, there is known a selective catalytic reduction (SCR) exhaust gas purification device that injects a reducing agent upstream of a reduction catalyst disposed in an exhaust gas passageway, causes the reducing agent to flow into the reduction catalyst together with the exhaust gas, breaks down NOx in the exhaust gas into nitrogen and the like, and releases the nitrogen and the like.
As one aspect of this exhaust gas purification device, there has been proposed a muffler of a structure that has the function of purifying NOx in the exhaust gas and forcibly turns back the exhaust gas flow direction inside. More specifically, as shown in FIG. 6, there has been disclosed a muffler 301 with an exhaust gas purification function where an oxidation catalyst 311 and an injection nozzle 312 that injects and supplies a liquid reducing agent are disposed in an upstream-side exhaust gas passageway 309, a reduction catalyst 313 and a reducing agent oxidation catalyst 314 are disposed in a downstream-side exhaust gas passageway 310, a ring member 315 disposed with holes 315a in its periphery is disposed in a turn-back portion 308, and exhaust gas is caused to flow downstream from the holes 315a to generate an exhaust gas flow along a turn-back portion wall surface 308a and create a vortex in the vertical surface of the turn-back portion 308 (see patent document 1).
Further, as another aspect of the exhaust gas purification device, there has been proposed an exhaust gas purification device for an internal combustion engine that has excellent exhaust gas purification performance and can be installed well in a limited installation space. More specifically, as shown in FIG. 7, there has been disclosed an exhaust gas purification device 401 for an internal combustion engine where both a DPF 413 and a urea deNOx catalyst 423 are disposed so that exhaust gas purification device can simultaneously trap particulates and decrease NOx in the exhaust gas, wherein the DPF 413 and the urea deNOx catalyst 423 are disposed in parallel (the flow of the exhaust gas is in series) and are communicated by a communication chamber 430 so that the entire exhaust gas purification device 401 is given a U-shape (see patent document 2).
Patent Document 1: JP-A-2005-273580 (claims, FIG. 1)
Patent Document 2: JP-A-2005-155404 (claims, FIG. 1)